1. Field of the Invention
This invention relates generally to the field of dental cameras, and more particularly to a dental camera system having at least two lenses selectable for either intra-oral or extra-oral use.
2. Related Art
For many years, clinicians in the dental industry used dental mirrors to more clearly visualize and diagnose hidden areas in a patient's mouth. These mirrors remain useful in certain respects, but significant limitations exist. First, it is often difficult to visualize a dental structure using dental mirrors, because the image must be reflected into the viewer's line of sight. Second, mirrors provide a relatively small image that can be difficult to see. Third, providing the lighting necessary to illuminate fully the area being reflected by the mirror remains a challenge. Furthermore, when using mirrors it is often difficult to communicate information to the patient or to other clinicians, because the image to be visualized is dependent upon the viewer's position relative to the mirror.
In order to address these and other significant limitations associated with using mirrors to visualize and diagnose areas in a patient's mouth, dental cameras were introduced into the field, and are now widely used within the dental industry to enhance the practitioner's ability to view the patient's dental anatomy. Dental cameras are also useful in providing the patient with a visual understanding of his or her clinical options.
Dental cameras provide advantages over dental mirrors in several respects. First, they do not require positioning towards a reflected angle. Second, they typically have built-in light sources which illuminate the area being visualized. Third, dental cameras are useful in obtaining a permanent record of the condition of a patient's mouth. Furthermore, they can be used as “teaching tools” to communicate information to others since the images appear on a monitor, and therefore more people than simply the dental practitioner may view their output.
Dental cameras typically comprise an internal base station that provides power, light and video processing to a handpiece, which contains an image sensor and optics. The light is typically provided via a flexible fiber optic bundle. Most dental cameras have one lens with a focusing mechanism that allows the dentist to view the near field for intra-oral use and the far field for extra-oral use.
The first cameras were merely adaptations of video endoscopes used in the field of medicine. U.S. Pat. No. 4,858,001 to Milbank et al. provides an example of an early dental camera. Milbank et al. discusses a hand-held endoscopic apparatus consisting of a body, a camera and a removable and interchangeable image-gathering element capable of presenting an image of an object to the camera. The image-gathering element, also called an objective element, may enable viewing of an image at varying angles because it may be flexible or rigid and may be of a variety of sizes and shapes. The objective element connects to a handpiece which has a hollow or tubular body portion rotatably carrying a central shaft upon which is mounted a video camera arrangement, such as, for example, a CCD mosaic chip camera. The tubular design is suited for penetration into the convoluted cavity of the human body.
Dental cameras, however, have particular requirements not addressed by most endoscopes. One challenge is to develop a camera suitable for both intra-oral and extra-oral imaging, each of which carries certain requirements which differ from the requirements carried by the other. For example, an intra-oral camera requires an illumination source and a wider angle as compared with an extra-oral camera.
U.S. Pat. No. 5,702,249 to Cooper made some early contributions to the field of dental cameras, taking these issues into account and creating a device more suitable to the applications for which it is used. Cooper discusses a modular intra-oral camera with a removable objective element that enables various lenses to be used interchangeably. Unfortunately, while the Cooper structure offers some flexibility, it also requires magnification changing means, aperture changing means, and light dispersion changing means to be coupled with the focusing means, thereby adding an unnecessary layer of complexity into the design of the camera. Furthermore, swapping the various objective lenses is clearly cumbersome for the dentist, and introduces a potential failure mechanism.
U.S. Pat. No. 5,771,067 to Williams et al. proposes an alternative design to Cooper. Williams et al. provides a dental camera including an adjustably focusing lens, and an electrically adjustable iris which may be progressively closed and opened to focus between the near field and the far field. More particularly, the iris is adjustable between a nearly closed opening and a wide opening in response to the focusing adjustment between the near field of focus and the far field of focus. Unfortunately, this strategy still requires the dentist to adjust a knob, which is a cumbersome task, particularly when the dentist is in the middle of a procedure.
Williams et al. also shares a disadvantage with Cooper, in that the location of the lens on the handpiece is fixed. More specifically, the location of the lens in these devices is on the distal tip, a location that is convenient for intra-oral use, but physically awkward for extra-oral use. In addition, imaging parameters such as white balance cannot be easily optimized for specific applications. Finally, in power constrained designs such as wireless cameras, the lamps that are required to provide illumination in intra-oral applications, but are not required for extra-oral applications, would often draw unnecessary power.
U.S. Pat. No. 5,381,264 to Wickholm et al. proposes another approach, namely a multiple field of view sensor lens assembly. The Wickholm et al. device includes a rotatable telescope for providing first and second fields of view for the sensor. In Wickholm et al., a rotatable lens assembly enables two objective elements with different fields of view to be placed at orthogonal planes to one another. Wickholm et al., however, suffers from many of the same disadvantages as the Williams et al. patent. Moreover, Wickholm et al. is not specific to, and not particularly suited for, the field of dentistry.
As explained above, providing a dental camera with the capability of effectively viewing the near field for intra-oral use and the far field for extra-oral use presents unique challenges due to certain inherent problems. Namely, the two environments have significantly different imaging requirements that cannot be easily accommodated by one lens system. First, the distance from the lens to the object is typically short intra-orally, but further extra-orally. Second, as mentioned above, the camera requires illumination intra-orally but not extra-orally. Third, the white balance compensation is different when the camera provides its own illumination (i.e., when the camera is used intra-orally) than when the illumination is from ambient light (i.e., when the camera is used extra-orally). Fourth, the optimal location of the lens on the handpiece differs for the extra-oral camera application as opposed to the intra-oral camera application.
Further challenges and differences relate to the aperture of the camera. The aperture is an opening in a lens that light passes through. Adjusting the size of the aperture controls the exposure level of the light. The wider the lens aperture, the more rays of light (photons) the lens can collect. A smaller aperture makes focusing less critical, and gives a lens a greater depth of field because it cuts off the more divergent beams of photons that would have to be focused. For intra-oral use a small aperture is desirable, in order to maximize the depth of field; whereas for extra-oral use a large aperture is typically desirable, in order to maximize brightness by letting more light into the camera.
It has previously been impractical to house these systems (with either one or multiple lenses) entirely within the handpiece, as the resulting camera would be too large and bulky. Most dental camera systems therefore suffer from limited portability.
There exists, therefore, a great need for a dental camera which takes an entirely fresh approach, and overcomes the above-mentioned obstacles which have heretofore plagued the prior art.